Carbon dynamics of wetland in the Sanjiang plain

Methane (CH 4 ) and carbon dioxide (CO 2 ) emission was measured from mires in the Sanjiang Plain, Northeast China, by using a static chamber technique during free snow-covered periods. The seasonal mean emission of CH 4 was 12.4mg/(m 2 ·h) and the emission range of CO 2 was 8.7–16.6g/(m 2 ·d) (gross CO 2 flux) during plant growth period. CO 2 emission rate in the day was stronger than that at night, and the daily peak appears at 19:00. The mire plants in the Sanjiang Plain begin to sprout at the end of April. The aboveground biomass of the mire plants increased from zero to the peak from July to September and showed single peak form. The aboveground biomass of Carex lasiocarpa (464.8g/m 2 ) was lower than that of Deyeuxia platyphylla (530.8g/m 2 ), but the underground biomass was higher than that of Deyeuxia platyphylla . Gross CO 2 flux showed the significance positive correlation relationship with plant biomass. Gross CO 2 flux and CH 4 emission were also correlated with soil temperature (0–5cm) and water temperature. However, the highest CH 4 emission rate lagged behind the highest soil temperature in the root area during plant growth period. The data also indicated that wet and warm conditions during the early spring led to greater value of CH 4 emission flux. Inundation is the necessary condition for the existence of methane bacteria, but there is no significant positive correlation between the inundation depth and CH 4 emission rate in this region. Within the same growing season and under the same inundation condition, the variations of CH 4 emission rate could be markedly different.